To understand why Facebook and Google have yet to ever agree on anything search related, we have to go back over two years. Keep in mind that most of this is fact-based and the rest is rumor and speculation; if I don't say anything, it's the former, but if a "source" is mentioned, it's the latter.

Furthermore, Microsoft, which by the way is a major investor in Facebook, also announced a global partnership with the social networking giant that would start by bringing Facebook status updates to Bing search results, but didn't reveal when it was coming. At the time, I wrote it made sense to start with Twitter because "Facebook has a significantly larger user base with many more status updates, and it's much easier to start small for something as new as real-time search."

Ever since then, strictly on the social front, Microsoft has been working hard with Facebook and Twitter while Google has been failing with both. Microsoft focused on working to bring social from the outside in and Google focused on brining social from the inside out.

Now let's take a look at Google. The search giant never convinced Facebook to come onboard. When its own Twitter deal was set to expire, Google launched Google+ in July 2011. Since this was a clear Facebook and Twitter competitor, negotiations for a renewal fell apart. Google claims Twitter walked away, while Twitter has not publicly given a reason as to why the deal was not renewed.

Fast-forward to this week. Google announces Search plus Your World (SPYW), which favors Google+ results over Facebook and Twitter. Twitter publicly criticizes SPYW, and the company even releases an official statement. Facebook employees react as well, but the company declines to comment. Google meanwhile says it would have been more than happy to treat Facebook and Twitter equally to Google+, but the companies aren't giving the search giant access to the data it needs.
So, how come Facebook and Google never managed to reach a deal? Journalist John Battelle of Wired fame tries to explain:

I've heard from a source with knowledge of the Facebook/Google negotiations over integration of Facebook's data into Google's search index. This source – who while very credible does come from Facebook's side of the debate – explained to me that during the 2009 negotiations, Google balked at Facebook's request that Facebook data be protected in the same fashion as it is in Facebook's deal with Bing. In essence, Google claimed no way to keep data within circles of friends in the context of a Google search.

According to this source: "Senior executives at Google insisted that for technical reasons all information would need to be public and available to all." But the source goes on to point out that in Google's own integration of Google+, Google does exactly what it claims it could not do with Facebook data. "The only reason Facebook has a Bing integration and not a Google integration is that Bing agreed to terms for protecting user privacy that Google would not," this source told me.

Also, and quite interestingly, Google also refused to agree to a clause which stated that Google could not use the data to build its own social network. Now, this is where things can get very dicey. It's very hard to prove whether or not a company is using the data in particular ways, and had Google agreed to that clause, it might have severely limited its ability to build Google+. What is clear is that Microsoft agreed to Facebook's terms.

Journalist Stephen Levy also from Wired heard the same thing via his own sources (or were they the same?):

Sources close to late 2009 discussions between Google and Facebook tell me that Google had the opportunity to integrate Facebook information in its search results–on the same terms that such content now appears in Bing. But, those sources say, Google refused, on the grounds that it could not technically provide the privacy protections required. Those privacy protections involved restricting social information only to people who users want to share with—basically what Google has now provided for users of its own service.

In summary, Facebook offered the same data deal to Google and to Microsoft. Microsoft agreed and Google didn't. It appears that both Facebook and Twitter were at certain points willing to give Google access to the data it needed, but Google refused to agree to certain terms.

Journalist MG Siegler not only confirms this angle via his own sources, but offers more information:

Prior to the launch of Google+, Facebook and Google were engaged in discussions to use Facebook data for presenting richer results on people searches. In other words, you'd search for a name and you'd see a result populated by Facebook data, including a picture of that person and what city they reside in, etc.

The two sides were so close to agreeing on this that Facebook even built a data feed specifically for Google to use, I'm told. But then, for reasons unknown at the time, Google abruptly pulled the plug on the idea.

Several months later… Google+.

Again, it looks like Google is painted as the bad guy. Google's side of the story is unsurprisingly different. "We want to set the record straight," a Google spokesperson said in a statement. "In 2009, we were negotiating with Facebook over access to its data, as has been reported. To claim that we couldn't reach an agreement because Google wanted to make private data publicly available is simply untrue."

Google is of course suggesting there is a different side to the story. Battelle follows up with more details:

Apparently, Google believed that Facebook's demand around public information could be interpreted as applying to how Google's own search service was delivered, not to mention how it (or other products) might evolve. Interpretation is always where the devil is in these deals. Who's to say, after all, that Google's “social search” is not a “social service”? And Google Pages, Maps, etc. – those are arguably social in nature, or will be in the future.

Google balked at this language, and the deal fell apart. My Google source also disputes the claim that Google balked at being able to technically separate public from private data. Conversely, my Facebook source counters that the real issue of public vs. private had to do with Google's refusal to honor changes in privacy settings over time – for example, if I deleted those soccer pictures, they should also be deleted from Google's index. There's a point where this all devolves to she said/he said, because the deal never happened, and to be honest, there are larger points to make.

All this comes down to who you want to believe. Both companies were acting in their best interest, and since both know social is the future of the Internet, they couldn't figure out a deal that would make them both winners. It's no surprise that Facebook and Google are reportedly blaming each other (although, not publicly, through anonymous sources) for the collapse of a potential deal: that's what happens when there's a lot on the table.

In the end, Facebook and Google have always been more enemies than friends. Just take a look at some of the articles below for what I mean. I don't expect this to change anytime soon.